Today, music is often generated using a data-compressed digital audio signal. As one of the data-compressed digital audio signal, MP3 (MPEG Audio Layer-3) is well known. The MP3 is one of compression methods for handling acoustic data using digital technology. Nowadays, the MP3 is widely used in portable music players and the like.
A popular digital audio signal such as the MP3 has a problem in that when a decompressed digital audio signal is directly subjected to analog conversion for output, attack sound (attack component) is deteriorated to damage sound quality. In order to cope with this, a digital signal processing device that amplifies a signal output of the attack sound is proposed (refer to, e.g., Patent Literature 1).
The proposed digital signal processing device compares a signal level of a predetermined frequency band extracted through a band division filter and a prescribed threshold level and detects a digital signal having a level equal to or higher than the threshold level as the attack sound. Then, the digital signal processing device amplifies the detected attack sound and synthesizes the amplified attack sound with a digital signal before band division to thereby enhance the attack sound.
As described above, the attack sound included in a predetermined frequency band can be amplified and enhanced in accordance with a signal level, so that when, for example, low-frequency attack sound is amplified, dynamism of powerful sound such as drum sound can be enhanced. When high-frequency attack sound is amplified, sound such as cymbal sound can be made clearer.
As described above, it is possible to make an output sound sharp as a whole by amplifying and enhancing the attack sound in accordance with a signal level. Thus, the proposed device can bring high effect for improvement in quality of a compressed audio signal, such as the MP3, in which the attack sound may be significantly deteriorated.